Telephone system



Jan. 7, 1941. R. E. coLLls ErAL TELEPHONE SYSTEM Filed June 17, 1938 9l Sheets-Sheet l E. COL L S /NVE/vrons: y By J-B NEWSOM ATToRN y Jan. 7, 1941. R. E. coLLls ETAL TELEPHONE SYSTEM Filed June 1'7, 1958 9 Sheets-Sheet -2 Jan. 7, 1941. R. E. coLLxs ETAL TELEPHONE SYSTEM FiledJune 17, 1938 9 Sheets-Sheet 5 Jan. 7, 1941. R, E, CQLLIS ETAL 2,227,488

TELEPHONE SYSTEM Jan. 7, 1941. R. E. coLLxs TAL TELEPHONE SYSTEM Filed June 17, 1938 9 Sheets-Sheet 5 coLL/s DEH/v Nvtman n.5. HERsEr .1.3. NEwsou mvm Jal'l- 7, 1941 R. E. coLLls Erm. 2,227,483

TELEPHONE SYSTEM Filedv June 17, 195s 9 sheets-sheet e gil sus. GROUP fw /NvE/vrons: R151 HERSE Y .1.3. NEWSOH NW3 ,YA

Jan. 7, 1941. R. E. coLLls Erm.

TELEPHONE SYSTEM Filed June 17. 19258 9 Sheets-Sheet 7 QN KNK DNN TELEPHONE SYSTEM Filed June 17, 193B 9 ShtS-Shet 8 FIG. 9

/NvE/vro/Ps: R15.' gpggy .1.8. AIL-Wsw Jan. 7, 1941.

TELEPHONE Filed June 17, 1938 R. E. COLLIS ETAL SYSTEM 9 Sheets-Sheet 9 IIT Wl-@ 11%? Id VES J. B. NEWSH Patented Jan. 7, 1941 .UNITED STATES PATENT oil-FICE TELEPHONE SYSTEM New York Application June 17, 1938, Serial No. 214,354

6 Claims.

This invention relates to telephone systems and particularlyto those in which automatic selector switches controlled by central-office register mechanisms are employed for establishing 6 conversational connections.

lt has been proposed heretofore, in systems using central-ofce register senders and common switch controlling markers, to extend calls over alternate route groups of trunks through a tan- 10 dem office to the called oiice in the event that all direct trunks from the calling oilice to the called oiiice are busy at the time they are tested. ln these prior systems the common switch controlling marker in the originating or calling of- 15 nce is provided with individual route relays for the several groups of direct trunks to called olhces, these `relays serving to cause the connection of the marker to the proper frames of the switches for testing the desired trunk groups 2li and also serving to establish in the sender the information needed thereby in the further ektension of the call. Where an alternate route group of trunks is provided to the tandem oice it has been necessary in these prior systems to 2li provide the route relay of the alternate group with the necessary information :for causing the marker to establish the connection in the origi hating ofce to 'trunks of such alternate route group and also to provide this relay with means 3d for giving the sender the routing information necessary for it to control the extension of the connection over the alternate route group and through the tandem oflice to the trunk group outgoing from the tandem office to the called 2id office. In effect this requirement necessitated the provision of a direct route relay for each direct trunk group and also an alternate route relay or the equivalent thereof for each direct trunk group that had an alternate route through .im the tandem office.

lt is, therefore, an object of the present invention to simplify the routing equipment in the central omce, to reduce the number of routing relays or equivalent mechanisms required there- 45 in, and otherwise to improve the operation of these devices and the systems in which they are utilized. y

According to a feature of the invention, these objects are attained by means of a system in 50 which the marker is equipped with individual route relays for each of the direct trunk groups outgoing to calledV or terminating offices and with a single route relay individual to an alternate group of trunks which serve as an alternate 55 route through the tandem ofllce for a plurality of the direct trunk groups. This simplification of the routing equipment in the marker is made possible by providing the direct trunk group relay with contact means for transferring to the sender the routing information for routing the call through the tandem oiice in case that becomes necessary. When the marker tests the direct trunks to the called office, the routing lnformation is transferred from the direct group route relay to the sender. If all the direct trunks are found busy by the marker, it cancels the route information which was transferred to the sender by the direct route relay and proceeds to operate the route relay individual to the alternate route trunks serving as an alternate route for the direct group. Since this V'alternate route relay is common to a number of direct route relays, i't cannot furnish the sender with information individual to any one of the direct groups. Therefore, this information, which will now be needed for extending the connection through the tandem omce, is again transferred to the sender by the direct route relay, which is still in its operated condition. lifter the idle trunk has been found in the alternate route group extendkd ing to the tandem oliflce, the routing informa tion transferred to the sender under the control of the direct route relay is utilized by the sender for controlling the switches in the tandem omce to select a trunk extending from the tandem du omce to the terminating omce in which the called line appears..

Another feature of the invention is a routing system of the kind above described in which the direct trunk groups are divided into :first choice ad subgroups and a second choice subgroup, a routing relay being provided for each such subgroup, and in which the alternate route trunks to the tandem omce are likewise divided into rst choice subgroups and a second choice subgroup, 0 each such subgroup being equipped with an individual route relay in the marker. The marker in testing for an idle trunk to extend a call to a particular terminating office will cause the operation of a rst choice direct `route relay, then the second choice direct route relay, then a first choice alternate route relay, and nally the second choice alternate route relay, testing the corresponding subgroups of trunks in succession until an idle one is found in some one of the \four subgroups thus available. The routing info\ ation for the called oflice is, as above explained, transferred to the sender under the control of the routing relay of the rst direct subgroup. If all of the trunks of this subgroup are busy and it is necessary to test the three successive subgroups, the routing infomation is canceled from the sender as soon as it is determined that the first choice direct subgroup is busy. Upon the succeeding operation of the second choice direct route relay the same routing information is again transmitted to the sender under the control of the contacts of the latter relay. If all of the trunks in this second direct subgroup are busy, the routing information is again canceled,and the marker proceeds to operate the route relay of the first alternate subgroup. Upon the operation of this relay the routing information is restored to the sender under the control of the contacts of the routing relay of the first direct subgroup. If all trunks of the first alternate subgroup are busy, the routing information in the sender is again canceled, and finally the alternate route relay of the second choice alternate group is operated, and once more the routing information is reestablished in the sender under the control of the contacts of the rst choice direct subgroup route relay. Thus the marker is capable of testing a succession of subgroups of trunks, some of which are direct route trunks and others of which extend over a common alternate route through the tandem oiiice. And as it performs these tests it establishes in the sender the information which will be necessary for the sender to control the further extension of the call in the event that an idle trunk in the subgroup undergoing test is found.

These and other features of the invention will be described more fully in detail in the following specification.

The detailed specification should be considered in connection with the accompanying drawings in which:

Fig. 1 is a diagram of the trunking plan` showing how a calling line may be extended through an originating oflice over the direct trunks or over alternate route trunks;

Figs. 3 to 10, inclusive, when taken in the order illustrated in Fig. 2, show in detail those portions of the circuits in the originating office which are necessary to a complete understanding of the invention;

Fig. 3 shows in simplified form a subscriber station, primary and secondary cross-bar line switches, primary and secondary district switches, primary and secondary sender link switches, a primary oice switch, links and trunks for connecting'the subscribers line through the switches to a sender, and connectors for connecting the district and ofiice switches to originating markers;

Fig. 4 shows in more detail one cross-point each of two secondary oiiice switches on oflce frame No. 0, oiilce links connecting them to the primary oice switch shown on Fig. 3, two outgoing trunks connected to the two cross-points and belonging to first choice subgroup A of the original route, and parts of the oflice frame connector for connecting the test leads of outgoing trunks to markers;

Fig. 5 shows that part of the subscriber sender which registers information supplied it by a marker, and which it requires to extend a connection forward over an outgoing trunk and to a terminating office. It also shows diagrammatically a connector for connecting senders to markers as required; and

7l Figs. 6 to 10, inclusive, show in detail those parts of a marker which are involved in this invention.

GENERAL DESCBIPTION or CIRCUITS AND EQULPMENT The invention is illustrated in an automatic telephone system in which automatic switches of the cross-bar type are used as the medium for extending connections from subscribers lines over trunks to other subscribers lines. These crossbar switching mechanisms are controlled by register senders at the central office, which receive the designations from the calling subscribers dials, and by decoder markers, which are connectable to the senders for receiving information from the senders, and which are connectable to the proper switch frames for the purpose of testing the outgoing trunks and for testing the connecting links and for operating the magnets of the cross-bar switches to establish the connections.

While the system disclosed is not limited to the use of cross-bar switches of any particular type, reference may be had to the patent toV Reynolds 2,021,329 of November 19, 1935, for an understanding of the construction and operation of a switch suitable for use in such systems. Because of the complicated nature of these systems, and since it is not necessary to an understanding of the invention that the system in all of its de tails be disclosed, much of the circuits and equipment has been eliminated in the present disclosure for the sake of simplicity. And in the following descriptions reference will be made to numerous operations which are not fully disclosed in all of their details. Wherever such references occur it will be understood that the circuits and equipment so referred to are already old in the prior art, and in particular reference is here made to the following for a detailed disclosure of all operations and equipment referred to herein but not specifically disclosed: Carpenter Patent No. 2,093,117V of September 14, 1937; and Carpenter application Serial No. 214,356, filed June 17, 1938.

General description of trunking plan Referring to Fig. 1, and assuming that the line of a subscriber originating a call has been connected through line switches to district junctor |00, and that the subscriber has dialed an oiTice code calling for connection to the terminating ofce |28 reached over the original route or over the alternate route outgoing trunks shown on the figure, the first preferred path is over either rst choice subgroup A or first choice subgroup B of the original route, the selection between those two subgroups being predetermined by a condition set up in the marker on its preceding engagement. 'Ihe second preferred path is over the common choice subgroup of the original route. The third preferred path is over either first choice subgroup A or first choice subgroup B of the alternate route, and the fourth preferred path is over the common choice subgroup of the alternate route. y

A connection over the first preferred path may be established by closing a cross-point in each switch mentioned, from district junctor |00, through primary district switch |0|, district link |02, secondary district switch |03, ofllce junctor |04, primary oiilce -switch |06, oilce link |08, and secondary office switch ||2 to outgoing trunk IIB in subgroup A or outgoing trunk ||8 in subgroup B. Or a connection may be made over the same path to one more trunk in each subgroup, connected to the same secondary oiiice switch H2;

tti

dit

titi

or through the same primary olce switch |06 but other oiiice links such as vand to other secondary otlice switches such as 3 to other outgoing trunks such as ||1'in subgroup A or ||9 in subgroup B, there being ten secondary omce switches in all on this omce frame No. 0, with twenty trunks in each'subgroup. 'I'he same secondary oflice switches and outgoing trunks may be reached through other primary oilce switches onI the same oilice frame No. 0, or through other secondary district switches and the same primary oilice switches. The twenty other outgoing trunks of each subgroup are connected to the secondary office switches of oce frame No. 1, equipped and arranged just like ofilce frame No. 0, and are reached through the same secondary district switches.

A connection over the second preferred path may be established over the same paths to the same secondary office switches, where different cross-points are closed to connect to the forty outgoing trunks of the common choice subgroup, such as trunks |20 and |2|.

Connections over the third and fourth preierred paths are established in precisely the same manner, except that the outgoing trunks oi the alternate route are connected to secondary offices switches on oflice frames No. 1 and No. 2. For example, a connection may be made from district junctor |00, through primary district switch |0|, district link it, secondary district switch |03, office junctor |05, primary oflice switch |01, office link lll) and secondary ofce switch H4, to outgoing trunk itt in nrst choice subgroup A, or outgoing trunk itil in rst choice subgroup B, or outgoing trunk itt in the common choice subgroup. The alternate route trunk group, which may serve a number of direct route groups, extends to the tandem ofiice itil. At the tandem oilice switches i130 are controlled from the originating offices to extend the calls over trunks |3i to the called oilices, such as orlice itt.

DETAILED DESCRIPTION ln the following detailed description, and in the accompanying drawings a certain grouping oi outgoing trunks is arbitrarily assumed for the purpose or illustrating this invention. The ex tension ot a connection is traced from a calling subscriber to another central oice than the one to which his line is connected, and the assumptions rnade are as follows: The direct or original route used by preferance, consists of one-hundred and twenty trunks extending directly toy the terminating ohfice, and divided into three subgroups of :torty trunks each, known as iirst choice subgroup A, nrst choice subgroup E and the common choice subgroup. The alternate route, used whenior any reason the original route is not immediately available, consists of one-hundred and twenty trunks extending direct to a two-wire tandem center, whence calls may be extended to any one of a number oi terminating oices, and is divided into lthree subgroups of forty trunks each, known as iirst choice subgroup A, first choice subgroup B, and the common choice subgroup. Each outgoing trunk connects to one whole level of a secondary ofce switch, and the forty trunks of any one subgroup occupy the same two adjacent levels in each of the ten switches on two adjacent oiiice frames. The three subgroups of the original route occupy three pairs of levels in office frames No. 0 and No. 1, and the three subgroups of the alternate group occupy the same three pairs of levels in oiilce frames No. 2 and No. 3. These assumptions, as stated above, are made for iilustrative purposes only, and in practice would vary to meet local conditions. The alternate route could be through any type of tandem center, either route could have more. or less than two first choice subgroups, any subgroup could have less than forty trunks, the six subgroups could all appear on one pair of office frames or on any number up to six pairs, the alternate route subgroups4 could appear on different levels from the original route subgroups, and any or all subgroups could occupy half levels instead of whole levels in the switches.

Referring now to the drawings, Fig. 1 shows in skeleton form the assumed trunking plan as described above. Figs. 3 to 10, inclusive; when taken in the order shown in Fig. 2, show in detail those portions of the circuits which are I necessary for a complete description of. the

Detailed description of a call Assuming that a call is originated by the sub# scriber at station 300, whose line 30| terminates on primary line switch 302, a train of operations is started which selects an available path to an idle sender, and operates select and hold magnets on the primary and secondary line switches and sender link switches to close that path from the subscribers line to the sender. This connection is shown through line link 303, secondary line switchy 304, district junctor 305, primary sender link switch 300, sender link 301, and secondary sender link switch 308 to the sender partly shown on Fig. 5. District junctor 30h also terminates on primary district switch 300.

The subscriber dials the office code of the desired terminating omce, and when the code is registered in the sender, relay tti operates and causes the sender to be connected to an idle originating marker through the connector shown at the left of Fig. 5, as for example by operating relays btt and ttt the sender is connected to the marker partly shown in Figs. 6 to 10, inclusive, over a plurality of conductors of which conductors btb to btb are shown separately, and. the remaining conductors are represented by the single line 000.

The cnice code is transmitted' from the sender to the marker, resulting in the operation of oirnormal relay 621 to supply certain operating and locking ground connections in the marker while it is engaged on this call, and of a certain .route relay, such as relay 102. Following relay 021, either relay 100 or relay 10| operates by a circuit from ground through bottom contact of relay 621, off-normal ground conductor 628, bottom break or make contact of relay 624, conductor 629 or 630, and winding of relay 100 or 10| to battery. Whether relay 100 or 10| operates depends upon whether relay 624 is normal or operated during the marker engagement, a condition which alternates from engagement to engagement, asA follows. If when relay 621 operates on a particular engagement it finds relays 624 and 625 normal, lground through its top contact will cause relay 625 to operate, but by shuntlng out the battery supply through resistance 623 to the winding of relay 624 will 5 prevent the latter from operating through the make contact of relay 62 5. Then when relay 621 releases at the end of the marker engagement it will break that shunt and relay 624 will operate through the make contact of relay 625, l through which contact relay 625 itself is also holding operated. Relays 624 and 625 will hold up while the marker is disengaged. When relay 621 operates on the following engagement its top contact will shunt out the battery supply l through resistance 626 to the winding of relay 625, which will thereupon release, but relay 624 will not release because it is held through top make contact of relay 621 and break contact of relay 625. Then When relay 621 releases at the end of the marker engagement it will break the holding circuit for relay 624 and that will release. Relays 624 and 625 will remain normal while the marker is disengaged.

Four route relays, 102, 103, 800 and 80|, may 26 be used in completing this call to its destination. Relay 102 is definitely assigned to the particular omce code which was dialed and no other; it operates when the oiice code has been received in the marker; it remains operated throughout 30 this engagement of the marker; it controls the testing of one of the rst choice subgroups of trunks of the original route to the terminating oilice; and it transmits to the sender information required for the extension of the call to the terminating office in case the original route is used, and some other information required in case the alternate route is used. Route relay 103 is also definitely assigned to the particular oice code and to no other; it operates in case no midle' trunk is found in the original route rst choice subgroup tested; it then remains operated throughout the engagement of the marker; it controls the testing of the common choice subgroup of the original route; and it transmits to the sender the same information as route relay 102. Route relay 800 may be assigned to several oiilce codes for terminating ofllces reached by alternate route through the same tandem center; it operates in case no idle trunk is found in the original route common choice subgroup; it then remains operated throughout the engagement of .the marker; it controls the testing of one of the first choice subgroups of trunks of the alternate route; and it transmits to the sender some information required for the extension of the call to the terminating cnice, additional to that transmitted by route relay 102. Route relay 80| is assigned to the same oiflce codes as route relay 800; it operates in .case no idle trunk is found in the alternate route rst choice subgroup tested; it

then remains operated throughout the engagement of the marker; it controls the testing of the common choice subgroup of trunks of the alternate route; and it transmits to the sender the' u the route relays are wired for flexible cross-conas indicated by the multiple strap 1|0, for exam- 1 nection according to the route and the trunks it controls, and so also are the contact springs of re1ays 100 and 10|. j

When route relay 102 operates it causes a subgroup of trunks to be tested and at the same time 5 it transmits information to the sender. The latter function will be described first.

Information to sender for -jirst preferred path Conductor 1|| is grounded from conductor 63| 10 through a break contact of relay 104 and make contact of relay 102, conductor 63| being grounded through a break contact of relay 6|0. It may be connected to either winding of any one of relays 900 to 909, thereby causing that relay to 15 operate, and if to its upper winding also causing relay 9|0 to operate in series. According to the relay or two relays operated, some or none of conductors 525 to 529 are grounded in one of twenty combinations, setting up sender relays 500 and 20 50| in one of four combinations, and relays 502, 503 and 504 in one of ve combinations. 'I'he record on relays 500 and 50| gives certain information as to the terminating oiice, which will be the same whatever trunks are used to reach 2 that oiice. The record on relays 502, 503 and 504 gives the cnice brush selection in the twowire tandem center in case the alternate route is employed, and although registered in the sender will not be used by it in case the original route 30 is employed. As shown for an example in the drawings, conductor 1| I is connected to the upper winding of relay 900, so relays 9|0 and 900 operate and ground conductors 525, 526 and 621, operating relays 500, 50| and 502, and leaving 3 relays 503 and 504 normal.

Conductor 1|2 is not grounded at this time because its connection from conductor 63| is not closed at the top make contact of relay |0||.

Conductor 1|3 is grounded from conductor 63| n through a break contact of relay 104 and make contact of relay 102. It may be connected to either winding of any one of relays |0|2 to |0|8, thereby causing that relay to operate, and if to its upper Winding also causing relay |0|9 to op- 45 erate in series. According to the relay or two relays operated, some or none ofv conductors 540 to 544 are grounded in one of fourteen combina.- tions, setting up sender relays 5|6 to 5|9 in one of seven combinations, with relay 5| 5 either operated or not operated. The record on relays 5|6 to 5|9 gives certain information as to the terminating oflice which will be the same whatever y trunks are used to reach that oiice. Relay 5|5 operated indicates a route through a tandem cen- 55 ter. As shown for an example in the drawings, conductor 1|3 is connected to the lower winding of relay |0|1, so that relay operates and grounds conductor 544, operating relay 5|9 and leaving relays 5|6 to 5|8 normal. Relay 5|5 is also left 60 normal because the original route is not through a tandem center.

Conductor 1|4 is not grounded at this time because its connection from conductor 63| is not closed at the bottom make contact of relay 106. 05

Conductor 1|5 is grounded from conductor 63| through a break contact of relay 106 and make contact of relay 102. It may be connected to either winding of any one of relays |000 to |009, thereby causing that relay to operate, and if to its upper winding also causing relay |0|0 to operate in series. According to the relay or two relays operated, some or none of conductors 535 t 539 are grounded in one of twenty combinations, setting up sender relays 5| to 5|4 in 75 one oi ten combinations, with relay 510 either operated or not operated. -The record on relays 61| to 514 gives information as vto the reslstances which the sender is to insertin the trunk to compensate i'or short trunks to the two-wire tandem center, if any, and again to compensate for short direct trunks or tandem circuits to the terminating anice. The set-up at this time is appropriate to the original route only. Relay 510 operated gives certain information as to the terminating omce. As shown for an example in the drawings, conductor 115 is connected to the lower winding of relay |006, so that relay operates and groundsconductor 501, operating relay 512 and leaving relays 510, 51|, 513 and 514 normal.

Conductor 116 is grounded from conductor 631 through a break contact of relay 106 and make contact of relay 102. It is connected to the winding of relay 911, thereby causing that relay to operate, which in turn grounds conductor 530, operating sender relay 505, which records the fact that there is no oillce selector ln the original route, and therefore the sender is to skip over the ofce selections when a connection has been established over that route.

If an idle trunk is found in that one of the original route iirst choice subgroups which is tested, then shortly thereafter relay |020 operates. That by grounding conductor 545 operates sender relay 520, the right-hand contact of which connects ground through a make contact of relay .52| to lock up both itself and those sender relays which were operated as described above, namely relays 500, 501, 502, 505, 512 and 519. The operation of relay 520 also causes the release of the connector relays 522 and 523, thereby breaking down the direct connection between the sender and the marker.

Testing outgoing trunks for first preferred path eral destinations, but which in the conditions assumed herein include just one subgroup of trunks to a single destination in each case, the marker has forty trunk test relays, of which only the first two'and the last two are shown, namely relays 612, 613, 616 and 611. There are also forty relays, one of which will be operated to designate the trunk selected for use, and of these also only the four are shown which correspond with the four trunk test relays shown, namely relays 619, 620, 621 and 622. Supposing 1- that relay 100 operates as described above on this engagement of the marker, then upon the operation of route relay 102, conductor 118 is connected to battery, and conductors 120, 123 and 124 to ground, through break contacts of relay 106 and make contacts of relays 102 and 100. Battery on conductor 118 operates relay 404, which is common to the pair of ofce frames numbered 0 and 1, and individual to the particular marker. 'Ihe operating circuits of the similar relays for the several markers, associated with one pair of oillce frames, are wired in a preference chain which is not shown, to prevent any two operating together, so that at any one time only one marker can deal with a particular pair of office frames. By grounding conductors 412 and 413, relay 404 operates relay 405 for ofce frame No. 0 which is partly shown in Fig. 4, and a similar relay for oice frame No. l, these relays also being individual to the particular marker.

ductor 635 to frame No. 1, where it operates relays corresponding to 406 and 401. Relays 405, 406, 401 and the corresponding relays in frame No. 1 connect the windings of the forty trunk test relays to the test conductors of the forty trunks of subgroup A of the original route, which trunks are connected to the two levels on each of the ten secondary switches on each of frames No. 0 and No. 1. Thus the Winding of relay 612 is connected through break contacts of relay 619, conductor 640 and make contacts of relays 405 and 401 to test conductor 414 of outgoing trunk 400, which is the rst of the group of forty. This trunk is connected to cross-point 402 and multiplied to the other cross-points in the same level of the same switch, that is, in the first of the two levels in the iirst of the ten switches on frame No. 0. The winding of relay 613 is connected through break contact of relay 620, conductor 641 and make contacts of relays corresponding to 405 and 401 in frame No. 1 to the test conductor of the next higher numbered trunk, which is connected to the rst of the two levels in the first of the ten switches on frame No. 1. The winding of relay 616 is connected through break contact of relay 621, conductor 642 and make contacts of relays 405 and 406 to test conductor 415 'of outgoing trunk 401, connected to cross-point 403 and multipled to the other cross-points in the same level of the same switch, that is, in the second of the two levels in the last of the ten switches on frame No. 0. The winding of relay 611 is similarly connected through break contact of relay 622, conductor 643 and make contacts of relays corresponding to relays 405 and 406 in frame No. 1, to the test conductor of the last of the group of forty trunks, which is connected to the second of the two levels in the last of the ten switches on frame No. 1. yThere are sufficient contacts on relays 405, 406 and 401, besides those shown, to accommodate the full set of twenty trunks per frame. The multiple straps shown connected to the contact springs of relay 405 indicate that the connected conductors multiple to corresponding relays associated with the same marker but other even-numbered oice frames. Those shown connected to the armature springs of relay 405 indicate multipling to corresponding relays in the same frame but associated with other markers. If outgoing trunk 400 is busy on a connection previously established, it is made so by crosspoint 402, or one of the others on the same level in the same switch, being closed. That grounds the test conductor 414 and causes trunk test relay 612 to operate, it having battery connected to the other end of its winding. In the same way al1 of the forty test relays which are connected to busy trunks will operate.

Conductors 123 and 124 are so connected as to block out of the forty trunks tested those which constitute the trunk group to the desired destination. Such a trunk group may contain any even number of trunks from two to forty. There are twenty relays similar to relays 6|| and 6|5, and by connecting conductor 123 to the winding of one of them and thereby causing it to operate when the route relay operates, the iirst trunk of the group irmarked. 'Ihere are also twenty relays similar to relays 6|4 and 6|8, and by connecting conductor 124 to the winding of one of them and thereby causing it to operate when the route relay operates, the last trunk of the .group is marked. Connecting conductor 123 to relay' 6| I, and conductor 124 to relay 6|8, as shown, identifies the trunk group as consisting of the entire fortytrunks which have been tested.

'I'he next step is to operate one of the forty relays like relays 6|9 to 622 to select for use the rst one of the forty trunks which happens to be idle. When relays 406, 401 and the corresponding relay in frame No. have operated to connect the forty test relays to the forty trunks, a circuit is closed from ground through front contacts of relays 406, 401 and 405, conductor 644 and the winding of relay 603 to battery, and the similar circuit from frame No'. 1 over conductor 645 to the winding of relay 604. Relays 603 and 604.

thereupon operate. Up to this time condenser 605 and resistance 606 in series have been shortcircuited and the condenser-timed polarized relay 608 has had opposing currents through its two windings, and the upper winding being stronger has held the armature on its back contact. One circuit is from off-normal ground conductor 628 through break contacts of relays 603 and 604 in parallel, and the upper winding of relay 608 to battery. 'I'he other circuit is from off-normal ground conductor 628 through the lower winding of relay 608 and resistance 601 to battery. When relays 603 and 604 have both operated, the direct ground connection to the upper winding of relay 608 is broken, but current continues to iiow through it for a time, charging condenser 605. As the condenser charges, this current dies down, until the lower winding overpowers the upper and the relay operates. This slow operation allows time for the trunk test relays, such as relay 62| to operate. Relay 609 has been operated from the beginning by a circuit from off-normal ground conductor 628 through break contacts of the forty trunk selecting relays, including relays 6| 9 to 622, and winding of relay 609 to battery. If out trunk 40|, for example, happens to be the ilrst trunk of the subgroup which is idle, trunk test relay 6|6 will be the first one normal, counting from the left, and its associated trunk selecting relay 62| will operate by a circuit from ground through make contacts of relays 608, 609, 6| I, 6|2 and 6|3, break contact of relay 6|4, make contacts of intermediate trunk test relays, not shown, and break contacts of intermediate relays, not shown, but similar to relay 6|4, break contact of relay 616 and winding of relay 62| to battery.

Relay 62| operating locks up through the back contact chain to its left, and at the same time breaks the back contact chain to its right, there'- by releasing relay 609. This breaks the circuit which operated relay 62| and thereby prevents the operation of any earlier relay vof the same kind, such as 6|9 or 620, in case an earlier trunk test relay, such as 6|2 or 6 I3, should release upon its trunk becoming idle.

Relay 62| operating also transfers the connection of the test conductor 4|5 from the winding of trunk test relay 6|6 to ground, thus immediately marking the trunk as busy.

Relay 62| operating also starts a chain 0f operations involving the operation of district and oice frame connectors 8|2, 3|3 and 3|4 to connect the marker to various parts of the district and office switches; the testing of all' possible paths fromprimary district switch 308 to the secondary office switch to which is connected outgoing trunk 40|; the selection of an available path such as the one shown through district links 3|5, secondary district switch 3|0, oiiice junctor 3|6, primary/ oiilce switch 3|| and oillce link 3|1; the operation of select and hold magnets in the primary and secondary district and oflice switches to close through this patli," thus completing a connection from subscriber) tation 300 to `outgoing trunk 40|; and the rel marker from service on this call.

If it should happen that relay 10| operates instead of relay 100 on this engagement of the marker, all operations would be as described above except that vfirst choice subgroup B of the original route would be involved instead of :lirst choice subgroup A. The corresponding armature springs of relay 10| are multipled to those of relay 100, and the four contact springs corresponding to those above mentioned on relay 100 are connected according to the pair of oflice frames and the pair of levels on which subgroup B appears, and to the section of forty trunks occupied by that subgroup. Under the assumptions made herein the office frames are the same for subgroups A and B, and the subgroup occupies the whole forty trunks with the test starting at the ase of the rst trunk in both cases, but the levels are different. Therefore, in this case battery is connected to conductor 1|8 and ground to conductors 123 and 124 as in the other case, but ground is connected to conductor 12| instead of to conductor 120. Therefore, all operations are the same except that relays 60|, 408 and 409 operate instead of 600, 406 and 401, connecting the marker trunk test relays to the proper pair of levels for subgroup B. Each office link, such as 3I1, is multipled to the ten cross-points in one vertical le of a particular secondary olce switch, so that the only difference in establishing a connection is that the select magnet associated with the proper level is operated.

In case all forty trunks of the rst choice subgroup tested are busy, all forty trunk test relays will operate, closing the circuit from contact of relay 608 clear through the chain of relays including 6|| to 6|8, to the Winding of relay 610,

and that relay will operate instead of relay 62| or a similar relay. Then relay 108 will operate by a circuit from ground through make contact of relay 6|0, conductor 632, make contact of relay 102, break contact of relay 106, and winding of relay 108 to battery. The inner top make contact of relay 108 operates relay 106 directly and relay 104 through the top break contact of relay |0|| over conductors 121 and 126. Relay 106 operating, breaks the battery and ground connections to conductors 1|8, 120, 123 and 124, releasing all connections between the marker and the office frames. All operated relays release which are shown on Fig. 4 and Fig. 6 except 609, 621 and 624 and 625 if operated. Relay 108 also released, but relays 100, 102, 104 and 106 remain operated, the two latter locking through top make contact of relay 106 to off-normal ground conductor 628. To prevent relay 6 0 releasing before relays 104 and 106 operate and lock, it locks through its top contact, conductor 633, outer top contact of relay 108, top break contacts of relays 104 and 106 in parallel, to conductor 628. To

locked up, relay 108 locks through its bottom makecontact and conductor 632 to the bottom vmake contact of relay 6I0.

When relay 106 releases, it closes a circuit from ground through its break contact, make contacts of relays 106 and 102, conductor 1|4, and the winding of route relay 103 to battery, causing the last to operate.

Information to sender for second preferred path.

found busy, and then permanently at the break y contacts of relays 104 and 106. Relays 9|0, 900,

IOI1, |005 and 9II thereupon release, and that causes the release of all the sender relays shown on Fig. 5 which had been operated through their contacts.

The operation of route relay 103 and the release of relay 6|0 causes'these same relays in marker and sender to re-operate, conductors 1I 1I3, 1I5 and1|6 being grounded again, this time Athrough conductor 63|, break contacts of relays 105 and 101, and make contacts of relay 103.

If an idle trunk is found in the original route common choice subgroup, relay I 020 operates, then relay 520, and that locks up, locks the record in the sender, and releases the connection be tween sender and marker, as described above in connection with the iinding of an idle trunk in one of the iirst choice subgroups.,

Testing outgoing trunks for second preferred path Route relay 103 operating closes circuits from battery and ground through break contacts of relay 101 to seize and test the original route common choice subgroup of out trunks. Since those are assumed to be on the same pair of oilice frames and to comprise forty trunks with the test starting at the first trunk, as in the case of the rst' choice subgroups, conductor 1|8 is connected to battery and conductors 123 and 124 to ground as before. Since this subgroup appears on a different pair of levels, conductor 122 is grounded. As a result of these battery and ground connections, relay 404 operates, causing the operation Y of relay 405 in frame No. and a similar relay in frame No. 1; relay 602 operates, causing the operation of relays 4|0 and 4I| in frame No. 0 and corresponding relays in frame No. l; and relays 6|| and 6I8 operate.

The trunks are tested and if an idle one is founda connection is established and the marker disconnected as described above. Otherwise relay 6 I0 operates again, causing relay 109 to operate by a circuit through conductor 632, make contact of relay 103 and break contact of relay 101. The inner top make contact of relay 109 operates relays 105 and 101 in parallel and they lock to off-normal ground conductor 628. Relay 101 operating breaks the battery and ground connections to conductors 1I8, 122 and 124, releasing all connections between the marker and the oflce frames. All operated relays release which are shown on Fig. 4 and Fig. 6 except 609, 621v and 624 and 625, if operated. Relay 109 also releases. Similar precautions are taken against the too quick release of relays 6|0 and 109 as were described above in the case of relays 6|0 and 106. Relays 100, 102, 103, 104, 105, 106'and 101 remain operated. When relay 100 releases it closes the circuit from ground through its break contact, make contacts of relays 101 and 103, and the winding of route relay 800 to battery, causing the last to operate.

Information to sender for third preferred path The ground connections through break contact of relay 6|0, conductor 63|, break contacts of relay 105 or 101, and make contacts of relay 103, to conductors 1II, 1I3, 1|5 and 1|6, and thence to the windings of relays 300, |0|1, |006 and 9H, are broken early at the break contact of relay 6 I 0 when that operates because all trunks of the original route common choice subgroup are found busy, and then permanently at the break contacts of relays 105 and 101. Relays 9I0, 900, |0I1, |005 and 9|| thereupon release, and. that causes the release of all the sender relays shown on Fig. which had been operated `through their contacts.

The operation of route relay 800 and the release of relay 6|0 connect ground through conductor 63|, break contacts of relay 802, and make contacts of relay 800 to conductors 806 and 601.

Conductor 806 may be connected to either winding of any one of relays |000 to |006, thereby causing that relay to operate, and if to its upper winding also causing relay |0|0 to operate in series. According to the relay or two relays operated, some or none of conductors 535 to 630 are grounded in one of twenty combinations, setting up sender relays 5|| to 5|4 in one of tencomblnations, with relay 5I0 either operated or not operated. The record on relays 5II to 5|4 gives information as to theresistances which the sender is to insert in the trunk to compensate for short trunks to the two-Wire tandem center, and again to compensate for short tandem circuits to the terminating oice. The set-up at this time is appropriate to the alternate route. Relay 5|0 operated gives certain information as to the terminating office as before. As shown for example in the drawings, conductor 006 is connected to the lower winding of relay |006, so that relay operates and grounds conductor 539, operating relay 5|4 and leaving relays 5I0, 5| I, 5I2 and 5|3 normal.

Conductor B01 is connected to the Winding of relay I0| I, thereby causing that relay to operate, which in turn grounds conductor 540, operating sender relay SI5, which establishes certain conditions requisite when a connection is to be made through a two-wire tandem center. v

Besides operating sender relay 5|5, the operation of relay |0|| has two effects in the marker. Its top make contact connects conductor 63| to conductor 125, thus grounding the middle bottom armature spring of relay 104 for the iirst time, and its top break contact causes relay 104 to release by breaking apart conductors 126 and 121. This release of relay 104 connects ground from conductor 63| through make contacts of relay 102 to conductors 1| I, 1|3 and 1I2. Ground on conductor 1| has the same effect as in its two previous applications, operating relays SIU and 900, which in turn operate sender relays 500, 50| and 502. Since the call is now to be routed through a two-wire tandem center, the information recorded by relay 502 being operated will be made use of this time. Ground on conductor 1I3 has the same effect as in its two previousv applications, operating relayV |0I1,

which in turn operates sender relay |9. Conductor 1 |2 may be connected to either winding of any one of relays 9|2 to 9|6, thereby causing that relay to operate, and if to its upper winding also causing relay 9|1 to operate. According to the relay or two relays operated, `some or none of conductors 53| to 534 are grounded in one of ten combinations, setting up sender relays 506 to 509 in one of ten combinations according to the olce group selection in the two-wire tandem center. As shown for example in the drawings, conductor 1|2 is connected to the upper winding of relay 9|3, so relays 8|1 and 9|3 operate and ground conductors 53|, 533, 534, operating relays 506, 508 and 509, and leaving relay 501 normal.

The reason for setting up oilice brush and oice group information through contacts of route relay 102 instead of contact of route relay 800, is that such information is individual to the particular terminating oice to which relay 102 is assigned, whereas relay 800 may serve for several terminating oflices, each with its own office brush and group selections.

If an idle trunk is found in that one of the alternate route rst choice subgroups which is tested, relay |020 operates, then relay 520, and that locks up, locks the record in the sender, and releases the connection between sender and marker, as described above in connection with Afinding an idle trunk in an original route first choice subgroup.

Testing outgoing trunks for third preferred gTOuP Route relay 800 operating closes circuits from battery and ground through break contacts of relay 802 and make contacts of relays 800 and 100, assuming as before that relay 100 is operated on this call, to seize and test the alternate route subgroup A of out trunks. Since these are assumed to appear on a different pair of office frames but on the same levels in the switches, and

to comprise forty trunks with the test starting at the rst trunk as in the case of the original route subgroup A, conductor 1|8 is connected to battery and conductors 120, 123 and 124 to ground. Battery on conductor 1|9 operates a relay on oilice frame No. 2 corresponding to relay 404 on oice frame No. 0, and thereafter all operations are the same as described for the first preferred route, using relays on frames No. 2 and No. 3 corresponding in all respects to those on frames No. 0 and No. 1.

If al1 the trunks of the alternate route first choice subgroup tested are found busy, relay 6|0 operates a third time, causing relay 804 to operate by a circuit through conductor 632, make contact of relay 800 and break contact of relay 802. The inner top make contact of relay 804 operates relay 802 and that locks to off-normal ground conductor 628. Relay 802 operating breaks the battery and ground connections to conductors 1|9, 120, 123 and 124, releasing all connections between the marker and the oiiice frames. All operated relays release which are shown on Fig. 6, except 609, 621, 624 and 625 if operated, and also all operated relays correspending to those shown on Fig. 4, and also relay 804. Similar precautions are taken against too quick release of relays 6|0 and 804 as were described above in the case of relays 6|0 and 108. Relays 100, 102, 103, 800, 105, 106, 101 and 802 remain operated. When relay 804 releases, it

closes a circuit from ground through its break `common choice subgroup of out trunks.

contact, make contacts of relays 802 and 800, and the Winding of route relay 80| to battery, causing the last to operate.

Information to sender for fourth preferred path When relay 6|0 operates because all trunks of the alternate route first choice subgroup tested are found busy, it breaks ground from conductor 63| and thereby releases relays |008, |00|, 9|1, 9|3, 9|0, 900 and |0|1, and then all the sender relays release, shown on Fig.'5 and previously operated through their contacts. 'I'he release of relay |0|| causes relay 104 to operate through its top break contact, and the action of relay 6|0 in breaking ground from conductor 63| and thereby from the conductors leading to the windings of relays |008, |00|, 9|3, 900 and |0|1 is supplemented by 'break contacts of relays 802 and 104 breaking those conductors.

The operation of route relay 80| and the release of relay 6| 0 -connect ground through conductor 63|, break contacts of relay 803, and make contacts of relay 80| to conductors 806 and 801. Ground on conductor 806 operates relay |008, and ground on conductor 801 operates relay |0||. Relay |0|| operating connects conductor 63| to the middle bottom armature spring of relay 104 and causes the same to release. This connects ground from conductor 63| through break contacts of relay 104 and make contacts of relay 102 to conductors 1| 1|2 and 1|3, operating relays 9|0, 900, 9|1, 9|3 and |0|1. These relays operated in the marker cause the same relays to operate in the sender as were just re.

Testing outgoing trunks for fourth preferred path Route relay 80| operating closes circuits from. battery and ground through break contacts of relay 803 to seize and test the alternate route Since these are assumed to be on the same pair of ofce frames and to comprise forty trlmks with the test starting at the rst trunk, as in the case of the alternate route first choice subgroup, conductor 1 9 is connected to battery and conductors |23 and 124 to ground, as before. Since this subgroup appears on the same pair of levels on frames No. 2 and No. 3 as the original route common choice subgroup on frames No. 0 and No. 1, conductor 122 is grounded. Battery on conductor 1|9 operates a relay on oice frame No. 2 corresponding to relay 404 on oce frame No. 0, and thenceforth all operations are as described for the second preferred route, using relays on frames No. 2 and No. 3 corresponding in all respects to those on frames No. 0 and No. 1.

If all the trunks of the alternate route common choice subgroup are found busy, relay 6|0 operates a fourth time, causing relay 805 to operate by a circuit from conductor 632, make contact of relay 80| and break contact of relay 803. The inner top make contact of relay 805 operates relay 803 and that locks to-off-normal ground conductor 628. Relay 803 operating breaks the battery and ground connections to conductors 1|9, 122, 123 and 124, releasing allv connections between the marker and the ofiice frames. All operated relaysrelease which are shown onFig. 6, except 609, 62,1 and 624 and 625 i! operated,

and also all operated relays corresponding to` relays sua and sul. to cnductor sus, which is dit connected to the winding oi a route, relay for overilow trunks, not shown. Similar operations to those described above then ensue in an endeavor to connect the calling line to an overflow trunk and to set up the sender relays shown on Fig. 5 accordingly.

In the foregoing description it is explained hcw the marker rst makes a test of the ilrst and second choice subgroups of trunks extending direct- 1y to the called oflice and, nding these all busy, then tests the first and second choice subgroups of alternate route trunks leading to the tandem office through which access may be had to trunks extending to the called oilice. Should the marker find an idle trunk in either of the twosubgroups of direct route trunks, it proceeds to establish the connection from the calling district trunk 305 `through the district and oillce switches to such idle outgoing trunk. Thereafter the sender acts to control the equipment in the called ofllce to further complete the connection to the wanted subscribers line.l Should, however, all direct group trunks be busy and should the marker locate an idle trunk in one of the two alternate route subgroups oi' trunks, it likewise proceeds to establish a connection from the calling district trunk 305 through the district and oflice selectors to the selected idle alternate route trunk which extends to a tandem center. Thereafter the sender, using the information which it has received from the marker in the manner already described, controls the selective switches in the tandem center to choose a trunk in the group extending to the called ofllce. After this trunk has been seized and the connection extended to the called oiilce. the switching equipment therein is further controlled to complete the connection to the wanted subscribers line.

What is claimed is:

l. In a telephone system, a calling oiilce having automatic switches therein, a plurality of terminating offices, a tandem oiilce having switching means therein, trunk groups extending from said calling office directly to the respective terminating offices, a common group of trunks extending from the calling otllce to said tandem office and serving as an alternate route for calls from the calling oiiice to said terminating offices, route relays in said calling oiiice individual respectively to the direct trunk groups extending to said terminating offices, circuit means controlled by the contacts of each of said route relays for causing the selective operation oi said automatic switches to extend a connection over the corresponding trunk group to the terminating office, a single route relay for said common alternate route group oi trunks, circuit means controlled by said common group route relay for causing the selective operation of said automatic switches to extend a connection over the common group to said tandem oilice, and circuit means controlled by the contacts of each of said direct route relays for controlling the operation of the switching means insaid tandem cnice to cause the further to the corresponding terminating oillce.

2. In a telephone system, a calling oillce having automatic switches therein, a plurality of terminating offices, a tandem oillce having switching means therein, direct trunk groups extending from said calling oillce to the respective'terminating offices, a common group of trunks extending from the calling oiiice to said tandem omce and serving as an alternate route for calls to said terminating ofiices, a marker in the calling oillce having individual route relays for the respective direct trunk groups to said `terminating offices and a single route relay for said alternate route group of trunks, circuit means controlled by the contacts of each oi' said route relays for causing the marker to selectively control the operation of 'said automatic switches to extend a connection over the corresponding trunk group, and circuit means controlled by the contacts of each direct route relay for controlling the operation of the switching means in said tandem oflice.

3. In a telephone system, a calling oiiice havf ing automatic switches therein, a plurality of terminating oflices, a tandem ofilce having switches therein, direct trunk groups extending from said calling ofiice tothe respective terminating oiices, a common trunk group extending from the calling oiilce to said tandem office and serving as an alternate route for calls to said terminating olces, trunks extending i'rom said tandem ofce to each of said terminating oilices, automatic switches in each of said terminating oillces, route relays in said calling oiiice individual respectively to the direct trunk groups, a single route relay in said calling oiilce for said alternate route group of trunks, circuit means controlled by the contacts of each of said direct route relays for causing the selective operation of the switches in said calling cnice to extend a connection over the corresponding direct trunk group to the terminating oice, circuit means controlled by the contacts of said alternate route relay for causing the selective operation of the switches in said calling office to extend a connection over the alternate group trunks to said tandem oice when all of the trunks of a particular direct route group are found busy, and circuit means controlled by the contacts of any one of said direct route relays When all of the trunks of the corresponding direct group have been found busy for causing the selective operation of the switches in said tandem oice to further extend an alternate route connection over one of the trunks leading from the tandem oiTice to the called terminating oillce.

4. In a telephone system, a plurality of groups of trunks, route relays individual respectively to said trunk groups, automatic switches having access to said trunk groups, means responsive to a call for causing the successive operation o1' said route relays, means controlled by the operation of each relay for causing a test to be made of the corresponding trunk group in search of an idle trunk to serve the call, means controlled by each operated route relay for causing the selective operation of said switches to extend the call over an idle trunk in the corresponding group, a designation register, means controlled by the contacts ci the route relay individual to a particular one of said groups for causing the registration of a designation on said register, means responsive to the subsequent operation of other ones oi said route relays for alternately canceling said designation and rendering the contacts of said particular route relay effective to reestablish the registration of said designation, and switching means controlled by said registered designation for causing -the further selective extension of a call over one of said groups of trunks.

5, In a telephone system, a plurality of groups of trunks, automatic switches having access to said trunk groups, a sender having designation registers therein, a marker for controlling said automatic switches, route relays in said marker individual respectively to said trunk groups, means responsive to a call for associating said sender with the marker and for causing the successive operation of said route relays, means controlled by the operation of each relay for causing a test to be made of the corresponding trunk group in search for an idle trunk to serve the call, means responsive to any one of said route relays for causing the marker to selectively control the operation of said switches to extend the call over an idle trunk in the corresponding group, means controlled by the contacts of the route relay individual to a particular one of said groups of trunks for causing the registration of a designation on the registers of said sender, means responsive to the subsequent operation of other ones of said route relays for alternately canceling said designation and for rendering the contacts of said particular route relay eiective to reestablish the registration of said designation on the registers of said sender, and switching means controlled by the sender in accordance with the registered designation for causing the further selective extension of a call over one of said trunk groups.

6. In a. telephone system, a calling oiiice having automatic switches therein. a called ofilce. a direct group and an alternating'route group of trunks for extending calls from the calling omce to said called oilice, switch controlling registers in said calling oilice, a route relay for said direct trunk group and a route relay for said alternate route group in said, calling omce, means effective when a call is received for said called omce for operating said direct route relay to cause the testing and selection of an idle trunk in said direct group, means controlled by said direct group relay for operating said registers to establish thereon information for use in the event it becomes necessary to extend the call over said alternate route group of trunks, means controlled by said direct route relay for canceling the eil'ect of the information registered on said switch controlling registers, means eilective if all of said direct trunks are found busy for operating said alternate route relay and for releasing the operated registers, means controlled by said direct route 'relay for reoperating said registers Without l canceling the effect of their operation, and means controlled by the operated alternate route relay and by the operated registers for extending the call over an idle trunk in the alternate route group to the called oilice.

RAYMOND E. COLLIS. JOSEPH W. DEI-IN. RALPH E. HERSEY. JAMES B. NEWSOM. 

